Oil resistance and weather resistance (in particular ozone resistance) are required for the outer layer rubber of hydraulic hoses and high-pressure hoses. These hoses very often have a brass-plated reinforced layer such as a brass-plated wire, so that the rubber composition applied to the outer layer rubber is also required to have adhesion to a metal such as brass during vulcanization.
Therefore, chloroprene rubber (CR)-based rubbers which are excellent in oil resistance, weather resistance and adhesion to metals during vulcanization have conventionally been used as the outer layer rubber of hydraulic hoses and high-pressure hoses.
However, in recent years, from the viewpoint of environmental control and in particular dioxin control, halogenated rubbers are used less frequently, whereas rubber mixtures of acrylonitrile-butadiene rubbers and olefin rubbers are being used for the material having oil resistance and weather resistance (see, for example, Patent Document 1).
Patent Document 1 describes a rubber composition comprising 20 to 80 wt % of an α,β-unsaturated nitrile-conjugated diene copolymer rubber, 18 to 60 wt % of an ethylene-α-olefin-nonconjugated diene copolymer rubber, and 2 to 20 wt % of an aromatic vinyl compound-conjugated diene copolymer rubber.
Patent Documents 2 to 5 describe that the adhesion to metals during vulcanization may be improved by the addition of a metal salt of an organic acid.
Patent Document 1: JP 62-172043 A
Patent Document 2: JP 2005-188607 A
Patent Document 3: JP 2005-188608 A
Patent Document 4: JP 2005-291281 A
Patent Document 5: JP 2005-291282 A